As known, laminates consist of two or more plastic films of the same or of different type, coupled between them or stuck together by means of an adhesive. Said laminates, and in particular those intended for packaging foodstuffs, may incorporate a film covered on one side by a metal layer, such as aluminum or a thin sheet of aluminum or other metal to maintain the organoleptic properties (freshness, flavor, fragrance, etc.), of the packaged product, thus preserving it from air and moisture contact.
To stick the above-mentioned films an adhesive is generally necessary which, besides a long "pot-life", a good "green tack" and high cross-linking rate, shows a good resistance to heat and water. Furthermore, the adhesive must be non-reactive with the materials of which the films consist.
The adhesive used heretofore have generally a restricted application field in that they do not possess at the same time all of the requisite properties. Thus, for instance, the polyurethane adhesives based on polyether-polyols, have a good resistance to water but a poor tack, especially green tack, whereas polyurethane-polyester adhesives have an acceptable tack, but a poor resistance to water.